The top answer seems to have the mentality of "screw the consumer" when it comes to versioning. If you have someone using version 1 of an api, when you decide to make it version 2, you're essentially breaking their app by having the reference change to the new one.
The answer even touches on the subject that it should be a permalink, yet they then say that a new version should be the same url as the old one, which means it's not a permalink! In my view, this is madness and potentially breaking for people using your api.
In my personal opinion, you should set out with versioning in mind from the start, otherwise by making even a slight change to your api, you change what the consumer receives, potentially breaking stuff.
It should be the same URL as the old one. Just not the same content type.
The user /u/john of version 1 is the same user /u/john of version 2. You don't want to break all links just because the client upgraded. Just reply with the appropriate format for the version the client is asking for.
The answer even touches on the subject that it should be a permalink, yet they then say that a new version should be the same url as the old one, which means it's not a permalink! In my view, this is madness and potentially breaking for people using your api.
In my personal opinion, you should set out with versioning in mind from the start, otherwise by making even a slight change to your api, you change what the consumer receives, potentially breaking stuff.